First, below are three videos provided by Skype. It includes an intro by Skype President Josh Silverman who espouses "integrated communications". Integrated communications, unified communications, what's the difference?
Anyway, the first video talks about making Skype easier to use, a redesigned user interface, improved video features, other new changes & features and perhaps most importantly, the fact that it is "beta". In fact, they are only releasing the Skype client "releasing it to a limited set of users as a way to begin the conversation with our community." So be forewarned a) that it's a limited beta and b) that it is missing some features in Skype 3.8 such as full history and contact groups. Skype Journal has a similar warning.
Conversation management is better in Skype 4.0. It displays a list of all the conversations you've got going on and lets you easily move in and out of conversations. A conversations button above the contact lists all the conversations users have active and users can simply click between them to pick up a conversation where they left off. According to Mike Bartlett, Director of Windows Product Management at Skype, "You can also pop your conversations out into separate windows if you prefer having different windows for different conversations."
Check out the videos. Oh and if you want to live dangerously, you can download Skype 4.0 beta here. (Windows only - Mac & Linux users need not apply)